The invention relates to a method and a device for producing press-rolled pipes.
Rotationally symmetrical parts (for example tubes) are required in the structural design of loaded parts in the construction of vehicles (for example bicycle/motorcycle construction) which should be as light as possible, but must have the necessary resistance torques at the loaded positions. For this purpose, with tubular structural parts, for example, the ends are reinforced on the inside, the wall thicknesses in the middle are reinforced on the inside, longitudinal ribs are applied to the inside or combinations of these measures are carried out. Because the outer dimensions of these tubular structural parts cannot be changed for structural reasons, these even being standardized in part (for example in the case of bicycles), these measures are basically applied advantageously to the inside of the tubular workpieces.
These measures for modification of the inner region of the rotationally symmetrical parts have already been known for a long time and are prior art. However, the measures necessary for this purpose are very costly and even today to some extent cannot represent, in practice, justifiable costs. In this way, a tubular structural part for bicycles with inner thickening of the tube ends on both sides can already be produced today. However, for this purpose several costly pulling procedures are required, and on every individual structural part. Because of the method-dependent tolerances dependent upon the method in the conventional production of these parts, any advantage in terms of weight cannot be used in full because of the large tolerance zone of, for example, the uneven walls (differences in wall thickness), because the smallest wall thickness must be considered in the structural calculation.
The generic DE-P 44 46 919 describes a method for flow turning internally geared parts, wherein a workpiece is arranged on a press mandrel, which workpiece is plastically deformed by means of the force loading of pressure rollers. The co-pressing method and the counter-pressing method are described in detail.
In this respect, press-rolling technology allows maximized use of weight advantages as a result of the very small wall thicknesses due to the very high highest levels of hardening of the materials used (steel, steel alloys, aluminium and aluminium alloys, titanium and titanium alloys, copper and copper alloys, special steels etc.) which are attainable and the extremely even thickness of the parts produced. In particular the method allows excellent surfaces to be obtained in the interior of the workpieces, i.e. there is very little roughness. This low surface roughness guarantees special protection against cracks which can start from internal notches in the event of, for example, overstressing. In addition, the method allows high reproducible levels of accuracy. Fluctuations within the workpieces are minimal.